Basics of Flash Photography
Four Fundamentals we must know

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Maximum Flash Sync Speed

We usually call it Maximum Flash Sync Speed because of our concern when using flash, but it's not about the flash — it’s instead a limitation of the focal plane shutter, and actually is a Maximum Shutter Sync Speed when trying to sync with the flash. The flash must wait to be triggered until the shutter is fully open to pass it (Sync meaning the flash triggers when the shutter is fully open). The shutter motion takes a little time to be fully open, so the flash has to wait until the far edge of the frame becomes open. Another problem is that for fast shutter speeds, the opening edge of the focal plane shutter starts closing before the far side is fully open. That “early start” of closing means the shutter is never fully open, which causes an unexposed black band in the picture (photos below), which is a limit on the fastest shutter speed that can sync with flash. The faster that the shutter design can fully open, the faster the maximum sync speed possible (before it starts closing). This description is continued below, and Wikipedia has some nice illustrations of the action of these two curtains.

Almost all of the DSLR cameras now have focal plane shutters covering the film or sensor plane like a curtain. The focal plane (FP) shutter is in the camera body instead of in each lens. Focal plane shutters have been used in the better 35 mm film cameras since the first Leica in 1925 (and focal plane shutters are even older than that), because they provide superior timing of fast shutters (and not being in the lens greatly simplify the lens mechanisms). The really big deal about focal plane shutters is their precise accuracy. They use two curtains across the sensor, called first or front curtain, and the second or rear curtain. The first curtain opens and then the second curtain closes. The delay between two the two curtain start times is the open shutter duration. The two curtains use the same drive motor, same gears, same curtain speed, for every shutter speed, be it 30 seconds or 1/8000 second. And the two curtains travel across the sensor in the same direction (first one opening, second one closing), ensuring the same exposure at both ends of the sensor. One simple precise mechanism, with one mode and one curtain speed. One curtain opens the shutter, and the second curtain follows to close it. And today, the shutter speed is controlled by a quartz crystal clock. No complicated speed switching or gearing.

The focal plane shutter exposure duration is determined by the delay between the two curtains starting. Which today, the timing is controlled by a quartz crystal clock (instead of a complex mechanical assembly using springs and gears), providing very fast and accurate 1/8000 second speed, and also a very slow 30 second speed (both extremes are very difficult for a coiled spring mechanism — those older mechanical shutters only could be used between about one second and maybe 1/1000 of a second, or more typically 1/500 second). This focal plane system is great for interchangeable lenses, because it only needs one good shutter in the body, instead of a shutter in every lens. And this is a better and more accurate shutter, but focal plane shutters do have the limitation of maximum shutter sync speed with flash.

CCD Exceptions: DSLR cameras now mostly use CMOS sensors and also use the better focal plane shutter, however many cameras using CCD sensors (almost all compacts and phones) save the cost of a good mechanical shutter by using the CCD sensor itself to also time the exposure (electronic shutter, without sync issues). This is a simple timer again, also using a quartz crystal clock. The CCD chip has to be switched off each frame anyway, to move the last picture out of it, so it's simple to also control the On time for the exposure. However, blooming can be a problem, since the sensor is uncovered to light longer. The camera might enforce an arbitrary sync limit, perhaps 1/500 second with flash (since there is so little light available from faster exposures). Early CCD DSLRs tried using this type of CCD electronic shutter, but the better ones always provided the focal plane shutter. But technically, any practical shutter speed will work with flash with a CCD shutter (called electronic shutter).

Today DSLR mostly use CMOS sensors, for which the sensors timing capability is slow and more difficult, so they instead use the focal plane shutter which always has a Maximum Sync Speed limit. However even so, for video mode of 30 frames per second, flash is Not involved, and the shutter just opens once, and then video frames do use the sensor timing.

The duration of electronic flash is extremely brief, but the shutter must be fully open first, so that all areas of the frame are exposed simultaneously. At focal plane shutter speeds faster than maximum sync speed, the shutter is not fully open, and we see a black unexposed band at the top or bottom of our flash pictures (because focal plane shutters are vertical travel today). If you rotate your camera to portrait orientation, you will see this dark band down the one long side. If the camera has communication with the flash to know it is present, the camera likely will not allow a shutter speed faster than maximum sync speed.

Beginners becoming aware of this sync limitation are often unhappy that they cannot use a really fast shutter speed with flash. But even if they could, a faster shutter speed like 1/1000 second would truncate the maximum power level flash duration which lasts longer, so closing while still bright, terminating the exposure, resulting in much less exposure. Which might still might be usable in some situations, but it would make automatic exposure calculation about impossible (because the flash power could not represent the flash exposure). The Nikon D1 camera did have a fast shutter with 1/500 second sync in 1999, but this feature was abandoned in future models.

HSS flash mode is an exception which can “sync” flash at any shutter speed. It is a very different mode than regular speedlight mode. The HSS flash is converted into a continuous light, meaning, which is simply turned On before the shutter opens until after it closes, so (like any continuous daylight or incandescent light), there simply is no sync issue at any shutter speed. But it has a cost — to be able to be on for the longer duration, the flash power is seriously reduced in HSS mode (see next page, What is HSS?).

Speedlight flash sync is limited to typically about 1/200 second, but being limited to this Maximum sync speed is really Not any issue in typical indoor ambient levels (the speedlight flash is faster than the shutter, and the ambient is several EV lower than the flash). The main purpose of HSS mode is to use wide aperture (like f/2.8) with flash in bright sun ambient, and bright sun at ISO 100 f/2.8 probably requires 1/4000 second shutter. HSS can do this, if it has sufficient power for a limited range.

So flash sync speed is an issue, often limited to around 1/200 second shutter speed in many DSLR cameras which use the better focal plane shutters. We show examples of that issue here.

The Nikon D300 and D8xx (and the D7xxx family too) use faster shutters with higher life expectancies, and these better grade shutters offer Maximum Sync Speed at 1/320 second, shown here. Their specs say 1/250 second, but they work well at 1/320 second. There is a warning in the manual about faster than 1/250 sec, which I interpret to mean that 1/320 might cut off a little of a long flash duration, which could apply to some studio flash, or to a speedlight if using its slower full power level.

All images are always inverted in the camera, the lens projects images upside down on the sensor, so the actual travel is the opposite direction (and note that the focal plane shutters on these two camera models are moving in different arbitrary directions). The illuminated area is the traveling open slit width, which is fully open over full frame only up to maximum sync speed. At faster shutter speeds, the rear curtain begins closing sooner to make the open slit be more narrow. The speedlight flash is fast enough to stop the moving slit. These pictures simply show that open slit. The Nikon D300 and D800 camera shutters move in opposite directions, up or down (and the direction of movement appears inverted in the image file).

D300 1/250 second

D300 1/320 second

D300 1/500 second

D300 1/1000 second

D300 1/2000 second

D800 1/250 second

D800 1/320 second

D800 1/500 second

D800 1/1000 second

D800 1/2000 second

Many camera shutters only sync flash at up to about 1/200 second. Any time you see a problem like this, just reduce your shutter speed, so that it does not exceed Maximum Flash Sync Speed (in your camera's specs for Flash Sync Speed, also called X sync). This is what Maximum Flash Sync Speed is, it is a shutter situation, about when that shutter is fully open. Maximum Flash Sync Speed is NOT a property of the electronic flash. Instead it is simply the fastest focal plane shutter speed that the front curtain is fully open, and the rear curtain has not started to close (slit is open wide enough to provide a full open frame for the flash). But sometimes radio triggers add a delay which causes the same maximum flash sync problems (to diagnose, try flash with and without the radio trigger. Also it might just be time for new batteries in the radio trigger).

Maximum Flash Sync Speed Details

The black band you see above may not always be fully black, you might see some detail in it if there is enough ambient to show it, but the band area will block the flash. The darker band may not always even be noticeable in bright sun, the bright ambient will illuminate that area pretty well. FWIW, if this were a full frame camera shooting into a cropped format, that might crop a narrow dark band off, so it might get away with a slightly faster shutter speed than if shooting full frame. The two shutters appear about the same speed here, but the full frame shutter has to travel 1.5x greater distance than the cropped APS-C shutter.

Both cameras above used the same 24-70 mm lens at the same 70 mm focal length. So yes, this example also shows the difference in the cropped and full frame view with the same lens. The cropped view appears as a telephoto illusion (frame cropped smaller by smaller sensor, but then also necessarily enlarged more to view at the same size again), and the full frame view is more wide angle (not cropped).

These samples were a Nikon SB-800 speedlight flash (fast flash - 1/17800 second at 1/32 power. If the shutter speed exceeded the Maximum Sync Speed, then the flash speed would freeze the shutter travel too, causing the black band). The flash exposure is not affected by shutter speed, where we are able to see it. However, this is regular speedlight flash mode, and is NOT Auto FP flash mode (next page). This flash was not in the hot shoe, and was instead triggered with a PC cord, so that the camera was unaware any flash was present, which would otherwise refuse to trigger the flash if Maximum Flash Sync Speed was exceeded.

If the Nikon camera can recognize that a flash is present, it will prevent exceeding maximum flash sync shutter speed with a flash, even in camera manual mode. If the flash is off camera or the brand has no communication with the camera (no flash known present), then no shutter speed is prevented.

An undetected flash (off camera on radio trigger or PC Sync cable, or a non-system flash (off brand or studio flash, etc) will not prevent this issue from occurring. I used a PC sync cord off camera to be able to take the too-fast shutter speeds above. The point is, with the exception of HSS flash mode, the shutter speed with flash should not exceed the maximum Flash shutter sync speed of a focal plane shutter.

Speaking of cameras today:
DSLR type cameras typically have focal plane shutters.
Medium format cameras may have focal plane shutters or may have leaf shutters in each lens.
Large format cameras typically have a leaf shutter in each lens.
The small cameras (phones and compacts) typically use an electronic timer to enable/disable the sensor, to act as the shutter and duration. These have no maximum sync issue, but do typically limit the shutter speed, as called Maximum Sync.

What is a Focal Plane shutter?

There is some repetition from here on, hoping it will help to get the idea across.

First, the simplest concept of a shutter is a large solid sheet that covers the sensor. It is opened by pulling it back towards say the left side of the frame to expose the sensor. Then it is closed again by returning it back to the right to cover the frame again. But for a fast exposure time, the time to open and close is a significant part of the total exposure. Specifically the right side of the frame is exposed more than the left side (opened first and closed last). The shutters that are actually mounted in lenses (called leaf shutters) are more complex, being several interleaving blades designed to all open and close more quickly, but still not in zero time.

A focal plane shutter is in the camera body, being two moving shutter curtains stacked in front of the sensor (like two roller window blinds). One curtain opens to expose the sensor to light from lens, and after a timed duration, the second curtain follows in the same direction, closing to cover it (left side opened first, and then closed first). This ensures the same exposure on all parts of the sensor. The same mechanism going the same speed operates both curtains. That makes the exposure duration (and effective shutter speed) simply be the delay between the two curtain start times (electronically timed today).

Flash is faster than the shutter, and it can simply occur anywhere within this fully open duration, but normal flash mode is synced with the front curtain becoming open. We do also have a later choice of Rear Curtain Sync which delays the flash until just before the second shutter starts to close, used to show for the blur trails with slow shutter speed. Regular front curtain sync would show the blur trails appearing after the flash as apparently leading the motion. Rear curtain sync shows the blur trails more naturally following the motion.

But to implement even faster shutter speeds, the second curtain starts closing before the first is fully open, tracking together to create a narrow slit between the two curtains, the open slit moving across the frame (actually down the frame today, the shorter travel is faster). This narrow slit reduces the exposure under it (of time duration equal to the difference between the two curtains start times), to be a faster shutter speed, which can easily be very fast, but a narrow slit cannot expose the full frame area from a fast flash of light. That problem is due to shutter speed exceeding the Maximum Flash Sync Speed.

A few descriptions of focal plane shutters are available. The Wikipedia link has an interesting section on history and improvements.

A very interesting photograph (a classic) using a focal plane shutter is this 1912 picture by Jacques Henri Lartigue. This is NOT a flash picture, there are no dark bands, the daylight ambient was continuous, constantly present during the exposure. The shutter slit's travel motion can cause distortion of a moving subject... different parts of the frame are exposed by a moving narrow slit at slightly different times, when things may have moved as the slit is moving too.

In this picture, the shutter slit was moving up in the picture (down in the camera, picture is inverted). The spectators and roadside poles are leaning left because this 4x5 inch camera was being panned right, following the race car. The spectator's feet were exposed earlier and their heads later (moving left in the frame as the camera panned by to the right), at slightly different times, due to the slit moving up as the camera panned right. But the car was going even faster yet, moving further right, ahead of the shutter in the frame, so it leans the other way. It was a large camera and shutters were slower in 1912, so motion may be exaggerated, but his classic picture is responsible for us imagining speeding wheels as being slanted ovals, at least in cartoon drawings. The narrow open slit can provide a very short (fast) exposure, but it takes much longer for this slit to travel across the large frame. Shutters are much faster today, but the fastest motion can still be an issue. See the HSS flash picture of the grinding disk on next page.

Here's the thing: The operation of focal plane shutters is more than just open and shut, the design is instead more eloquent. There are two shutter curtains. The first curtain (moving across the frame, opening the frame to light) opens at the frame leading edge early, and uncovers the far edge last, giving unequal exposure across the frame. This worked for the photographers in the late 1800s who used their lens cap for the shutter, as the difference was insignificant for the few minutes of exposure times necessary then. But it would become significant in the short shutter times today. Two curtains solve the problem that IF this same curtain did open for the exposure, and then later reverse and close to end the exposure, there would be unequal exposures on the two sides of the frame (unequal by the two directions of shutter travel). But instead in a focal plane shutter, a second curtain, moving identically in the same direction and same speed to close the frame, closes the same leading edge first and the far edge last, the same movement action of the first curtain, so the two curtains even it out, the two effects add to be an even exposure at all points over the frame. The mechanical speed of the curtain does not affect exposure, and it is the same movement for any shutter speed. The exposure of any area of the frame occurs at different curtain travel times, but exposure duration only depends on the width of the open moving slit, which simply depends on the delay between start times of the two curtains. The delay of second curtain start time is the exposure time, which today can be timed precisely with an electronic crystal clock chip. Plus the total exposure also adds any time that both shutter curtains are held fully open (for a longer delay), while not partially blocked by either curtain. The curtains move vertically today, for shorter travel time and a faster shutter speed.

But, it does cause a limitation on flash sync, because flash pictures can only expose the full frame after the shutter is fully open. The front curtain takes a certain time to travel to the fully open position (and the rear curtain the same time to close again). So this curtain opening time (technically plus the brief flash duration time) is the duration of the Maximum Flash Sync Speed. Faster shutter speeds (shorter durations) will have already started closing earlier, blocking the flash exposure from the covered portions of the sensor. The curtain speed is WHY flash is typically limited to around 1/200 second (5 milliseconds) shutter speed on focal plane shutters today. Modern shutters became faster, flash sync was 1/60 second until about 1980. But materials are better today, and another speedup is that it is faster for shutters to move vertically down the sensor short dimension instead of horizontally across the long dimension.

Maximum Flash Sync Speed is most likely no issue indoors (dim or insignificant indoor ambient, and the flash will stop the action). Outdoors, it is only an issue if you want a shutter speed faster than Maximum Flash Sync Speed (which is typically around 1/200 second, which means in bright sun, fill flash may have to use f/11 for ISO 100).

Electronic shutters (like in compact cameras, simply timed by the CCD sensor chip turning on or off) are not limited about sync speed. Their flash can work at any speed, however most do still specify something like about 1/500 second maximum (fast cuts off the flash exposure of the tiny flash too). Iris shutters (in lenses of larger cameras) can sync flash at 1/500 second, or really any faster speed too, however if really fast, their opening and closing speeds (opening from the center) can expose the center area more than the corners.

Focal Plane Shutter Maximum Sync Speed

For those interested in the Numbers of focal plane Maximum Shutter Sync Speed.

There are two focal plane shutter curtains in front of the camera sensor (film or digital). The first curtain is normally closed, and the second curtain is normally open, which sum is no light exposure at all. Nikon calls them Front and Rear curtain. Canon calls them First and Second curtain. Same thing. These are rotary roll-up curtains, much like the old rollup window shades. Early cameras used fabric curtains, today a thin titanium foil curtain is used for durability.

At the shutter button, the first curtain opens by retracting to move across the frame (they move up and down today, it's faster). At first instant, this exposes only the leading edge of the frame, and the rest of the frame is dark, but which gets light after the shutter moves to open more. Let's say the shutter opening travel time to be fully open is X milliseconds (always the same travel speed at any shutter exposure time). Then at that instant of being fully open, the leading edge of the frame has been exposed X ms, and the far trailing edge essentially 0 ms. If at that same instant (of being fully open to pass flash, called sync), then the second curtain starts to close, moving in the same direction. Portions of the frame are still receiving light until the closing shutter passes them (exposure is the sum of the two curtains being open, so to speak). So specifically, the leading edge gets X ms exposure from the first curtain opening, and gets 0 ms more from the second curtain starting to close. The far trailing frame edge gets 0 ms from the first curtain opening, and X ms from the second curtain eventually closing. The two curtains accumulate an even exposure time over the entire frame, which exposure equals the travel time X (if we require an instant when the frame is fully open, for a flash).

This travel time X is the Shutter Speed exposure until the instant where both curtains are fully open, to allow flash to fully pass. Today, this is commonly a 1/200 second exposure which is called Maximum Sync Speed. 1/180 second is seen, as is 1/320 second also seen, in a few models. Faster traveling shutter curtains support a faster sync speed. Maximum Sync Speed is the exposure time required for the first curtain to become fully open, since any less exposure means the second curtain has already started closing (no fully open position).

For faster shutter speeds, the second curtain starts closing before the first curtain fully opens. For a 1/2000 second shutter speed, the second curtain starts closing 1/2000 second after the first curtain starts opening. This is a 1/2000 second exposure of all points in the frame, but the shutter becomes a narrow slit moving across the frame (the slit exposes for 1/2000 second), which will block flash except in that narrow slit.

For longer shutter speeds, say one second exposure, the second curtain simply waits one second before starting to close. The shutter is fully open all of that time.

However, the total shutter travel time (as opposed to exposure of the moving slit) is the travel time of the first curtain fully opening, and then the time of the second curtain fully closing, or 2x the travel time of one curtain (speaking of exposures at least as long as maximum shutter sync speed, when the shutter does fully open instead of just a narrow slit moving across). Note this is just shutter motion, and NOT exposure time. Continuous light, like HSS flash, has to stay on illuminating for that total time, double the Maximum Sync Speed duration for any shutter speed. That duration is why the HSS power level has to be significantly reduced, lower than speedlight flash mode.

Distortion of objects: But (for faster shutter speeds when it becomes more significant), the leading edge is exposed earlier in time than is the trailing edge, which fast shutter speeds can distort motion captured during that time. The leading and trailing edges are exposed the same duration, but at slightly different points in time.

Advantage of focal plane shutters: The same remarkable precision mechanism moves both curtains, creating and moving a virtual narrow slit of opening across the frame at a fixed speed, to provide precise fast exposures under that slit. There are really good reasons better cameras provide the focal plane shutter.

Downsides of focal plane shutters

How Fast is Maximum Flash Sync Speed?

The flash is often relatively nearly instantaneous, but it has to be synced to trigger when the shutter is fully open. For focal plane shutters, the fastest shutter speed at which the full frame is all fully open at any one instant (to allow instantaneous flash to fully cover the entire frame), is called the Maximum Sync Speed. The Nikon spec charts in rear of camera manuals call it Maximum Flash Sync Speed, and I often tend to say Maximum Shutter Sync Speed (all the same thing, sync of the flash to the fully open shutter). Flash sync is not possible if the focal plane shutter speed is faster than this limit (because some of the frame would be covered by the closing second rear shutter, and so unexposed, causing a dark band in picture). Some cameras use leaf shutters in each lens, or electronic shutters in some camera sensor chips, and these can sync faster than focal plane shutters (because there is always a fully open instant).

The Maximum Sync Speed for a focal plane shutter relates to how fast the curtain can move across the frame, to the Fully Open position. The flash has to wait for the fully open position, which determines Maximum Sync Speed, because if faster, the second rear curtain has already began to close.

In the 1960s, the focal plane shutter maximum sync speed was 1/60 second. Maybe 1/80 second in the 1980s. Today, shutters are faster, and 1/200 second (5 ms) is common today. A few models can do 1/250 second (4 ms) or 1/320 second (3.125 ms). Full frame cameras must travel half again farther than the APC-C sensors, but the vertical shutter travel today covers 1/3 less distance than horizontal. Full frame covering 24 mm in 3.125 ms travels 7.7 meters/second. Cropped APC-S covering 16 mm in 5 ms travels 3.2 meters/second. There is no Minimum shutter speed — any slower shutter speed can always be used with flash. However most camera automatons arbitrarily force about 1/60 second Minimum Shutter Speed With Flash in camera A or P or Auto modes (E2 menu on some Nikon models). This is not about sync or exposure, it is simply a concern about hand holding slow shutter speeds. Slow Sync or Rear Curtain Sync modes will bypass that limit to allow any slow shutter speed actually metered.)

The Nikon specs clearly say Maximum Sync is still 1/250 second on their faster shutters, but some of these models provide a mode to allow 1/320 second sync, warning it might suffer reduced range of the flash. My guess is this is not about sync, but means the fast shutter could cut off slow flashes, like some large studio flash at low power, or speedlights at maximum power (but any speedlight power level lower than maximum should not be any issue). The speedlight T.1 flash duration at maximum will about 3x longer than T.5 (typically around 1/300 second). Maximum sync speed is normally not a speed problem (at normal ISO and apertures, when the ambient is not contributing much), because the flash is faster, so maximum sync speed is perfectly fine. The speed concern is about daylight level bright ambient, unable to use faster shutter speed.

Even in camera Manual mode, the camera will not allow you to choose these fast shutter speeds if it knows the flash is present (if flash is on the hot shoe for communication). But a PC sync cord will not know any flash is present, and this example above used a PC sync cord (flash not in hot shoe), to prevent communication, to fool the camera into allowing any shutter speed. There is no reason to do that, other than to show the problem here. An APS-C sensor crop exposed on a full frame camera may crop off a small dark band, so it might get away with a slightly faster shutter speed than if shooting full frame.

Historically in the distant past, the only way to get around this sync problem with a faster shutter was to use a special flashbulb (named FP sync, for focal plane) that burns slower and longer to stay fully illuminated much longer, perhaps 1/30 second delay to peak, and then 1/30 second duration at half power points, for the full shutter travel time — more like continuous light for the longer shutter duration. HSS flash is the same similar solution today, a flash duration lasting as long as the shutter travel time (next page). This longer duration simulates continuous light, which has no sync requirement.

FWIW, speaking about historical details no longer important today, but the term flash sync used to have a different meaning. The flashbulbs took several milliseconds to fully ignite and become bright, so they had to be triggered before the shutter, and the shutter had to wait for them until they became bright. So other than the FP sync flash bulbs, the common camera sync modes were: So better cameras used to normally have a switch for F, M, X (and maybe FP) sync, to select your flash sync type. This is why today's camera still specifies X Sync (for electronic flash), but our concern now is about the maximum shutter sync speed.

Flash bulbs had guide numbers on the package too. For shutters that were not focal plane, they could use faster shutter speeds, but which cut off their longer light duration, so their guide numbers were typically maximums for 1/30 second shutter, and sometimes also a couple of stops less light at 1/250 second.

The Problem with Fill Flash in Sunlight

The shutter speed limit of Maximum Sync Speed is really no big deal for flash indoors. The flash is fast itself, so in dim ambient light (where we need flash), it matters less what shutter speed is, the flash is faster. The dim ambient is too dim to blur motion seen by a slow shutter, and indoors (if low ISO), we can open the aperture as wide as we wish without concern about overexposing the ambient. But this maximum sync speed becomes a much bigger problem when using fill flash in bright sun (because overwhelming bright sun cannot be ignored). The speedlight is extremely fast in dim light with no ambient to blur anything, but the bright sun is continuous, not fast.

The Sunny 16 Rule says at ISO 200, exposure in bright sunlight is 1/200 second at f/16. Bright sun does not vary, so this is the norm we expect. And we pretty much have to correctly expose the daylight scene. We cannot ignore the sun like we can ignore dim indoor illumination. Continuous light (like sunlight) has no shutter sync requirement, but when we add a flash for fill, now there is one. The topic of fill flash in sunlight is covered in Part 4.

With flash in sunlight, we cannot use faster equivalent exposures, like 1/400 second at f/11, or 1/800 at f/8 because the focal plane shutter's maximum sync speed is 1/200 or 1/250. That means, if using flash in bright sun at ISO 200, the camera exposure WILL NECESSARILY BE around 1/200 second at f/16 (Sunny 16, but cannot exceed sync speed). The f/16 requires a lot of flash power, but otherwise this works fine, unless you just craved to use f/2.8 out there. Camera P mode knows all about this, and has ability to set both shutter speed AND aperture, and so it is a good choice for fill flash in bright sun. But if you use camera A mode, and set f/4 out there without thinking, the camera will just fuss warning HI at you, until you set near f/16 so it can work in bright sun (at the limited sync speed).

Wishful thinking, but our dream is that if somehow we could increase shutter speed, we could open the aperture, for reduced depth of field, or to an equivalent exposure for daylight which lets the regular flash mode work at lower power level, without affecting either exposure. Or, a faster shutter speed could help the flash to "overpower" the sun, reducing the sun without affecting the flash — if we could, but we cannot (in these bright sun cases.). We are up against the maximum shutter sync speed wall. FWIW, using lower ISO, or using a Neutral Density filter, can allow a wider aperture in that case, but that's all it does (maximum shutter sync speed is still enforced). But these affect both the flash and the sun equally, so these do not change the balance between flash power and sun. We can only use more flash power to affect the balance, and then exposing the higher flash power might end up at f/32, which does decrease the sun that needs f/16, but we still need Maximum shutter speed sync. Flash in bright sun is a special case.

Ifs and Buts - Other Shutters, and Exceeding Maximum Shutter Sync Speed

Flash sync speed is really only an issue in bright sun. It is unimportant in dimmer light, where we need flash. So we might as well get used to Maximum Shutter Sync Speed, because it has always been this way, since the first Leica 35 mm camera in 1925 (focal plane shutter). The first Nikon F (1959) sync'd flash at 1/60 second. The situation is better today than it has ever been before.

One workaround in sunlight is to underexpose the sunlight ambient by a couple of stops, so the flash can stop the motion without the ambient blurring it again. Flash becomes main light instead of fill. Sports action likes this, it highlights the subject better anyway. The speedlight is faster than the shutter, and reducing the sun's exposure causes less blurring of action. And speedlights are the way High Speed Photography is done.

A couple of confusion factors which do not change the basics:

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